For many years funicular or cable car systems have used one of two techniques to allow the grip assembly for the car or carriage to pass over the support sheaves for the haul rope. Most typically, the funicular haul rope is lifted from the support sheaves as the cable grip passes over the sheaves. U.S. Pat. Nos. 4,092,929 and 3,797,407 illustrate this approach in modern funicular systems, while U.S. Pat. Nos. 440,001, 511,596, 536,611 and 546,955 illustrate haul rope lateral shifting and/or lifting approaches as applied to older funicular systems.
The second approach which has been widely used is to displace the haul rope supporting sheaves away from the haul rope as the grip passes along the drive path. Thus, in U.S. Pat. Nos. 332,934 and 404,498 the rope supporting pulleys are displaced or depressed as the grip passes. In U.S. Pat. No. 482,279 both lifting of the haul rope above stationary support sheaves and displacing selected sheaves are used.
The primary disadvantage of relative displacement between the haul rope and haul rope supporting sheaves in order to allow a funicular grip to pass over the sheaves is that once the haul rope is separated from the sheaves it is not possible to control or contain the haul rope in a positive manner. Thus, in conventional funicular systems some provision must be made to guide the vehicle or car to control its position when the haul rope is no longer confined by the guide or support sheaves. In horizontal curves, for example, lifting of the haul rope requires auxiliary guide wheels or tracks and wheels having flanges that will prevent the car from pulling the rope laterally out of alignment with the guide sheaves. Moreover, any time a haul rope is lifted from a support sheave, the risk of deropement of the rope from the sheaves is increased. Still further, relative separation of the haul rope from the support sheaves and its subsequent replacement can tend to produce twisting or spinning of the haul rope, which is detrimental to the sheaves, grip assembly and haul rope itself.
A further significant disadvantage which results when haul ropes are lifted, in some cases by as much as 20 inches, is that the stresses on the car or vehicle undercarriage is substantial. Thus, undercarriages must be relatively strong and undesirably heavy to withstand this stress.
In any funicular system employing an endless, looped haul rope there will be at least one rope splice between opposite ends of the haul rope. Rope splices typically require interweaving of alternating strands from the opposed ends over a length of about 1200 rope diameters, and the effectiveness of the splice depends upon the tendency of the strands to pull in radially against each other and the ends which are positioned where the rope core normally would be. Such haul rope splices, however, tend to fatigue earlier than the remainder of the haul rope, particularly in shuttle funicular systems in which the splice passes over the bull wheels at opposite ends of the system. A common concern in funicular systems, therefore, is haul rope splice fatigue.